The proposed research will investigate the molecular events involved in the proliferative actions of estrogen in breast cancer cells. We will investigate the MAPK signal transduction cascade as a potential pathway utilized by estrogen to cause the hyperplasia of breast cells. This could potentially lead to the identification of molecular targets for the actions of estrogen in breast tissue against which to generate new pharmacotherapies for the treatment or prevention of breast cancer. The physiologic and/or morphologic effects of the estrogen induction of the MAPK pathway has not yet been investigated in any cell type and therefore presents a logical starting point for the investigation of the means by which estrogen induces the proliferation of hyperplasia of breast/breast cancer cells. These studies will be accomplished by utilizing standard proliferative assays (MTS and 3H incorporation) to measure the growth of human breast cancer cells (MCF-7) in response to estrogen treatment. Direct measurements of MAPK or MAPK related enzymatic activities will also be performed. Mutant MAPK enzymes will be transfected into MCF-7 cells to determine if their activity is necessary for the proliferative effects of estrogen. The genes that are turned by initiation of the MAPK cascade such as cyclin D1 will then be evaluated.